This invention relates to implantable infusion pumps for the dispensing of infusates. In particular, it relates to a pump operating at positive pressure to dispense medication from multiple reservoirs in accordance with different specified flow rates. The device is capable of delivering easily and precisely dosed medication from any one or any combination of two or more reservoirs without complex pumping and flow control mechanisms and has the capability of mixing and/or diluting medications.
Implantable infusion pumps are currently used for a variety of medical purposes. Two classes of such commercially acceptable are generally referred to as “constant flow” and “programmable” pumps. Typical of the constant flow device is the Fluent™ pump. Constant flow devices are implanted in the human body and, in a typical configuration, rely on a liquid/vapor equilibrium to maintain constant pressure on the drug which is housed therein so that the drug flows through a capillary (flow restrictor) in order to maintain a constant flow rate. Such devices are used in a variety of medical applications, for example, to dispense chemotherapy at a relatively constant flow rate. As background to the Fluent™ device are U.S. Pat. Nos. 7,108,686 and 6,764,472.
There are medical conditions where a patient requires an adjustment in the dosage or requires a bolus infusion and as such, constant flow pumps are inadequate. Typical examples are the use of implantable pumps to treat chronic back pain and/or spasticity as seen in multiple sclerosis. In such cases a programmable pump is used to achieve proper flow rates over the spectrum of desired rates. An example of such a device is the Prometra® implantable programmable pump. The pump has a refillable drug reservoir that is maintained at constant pressure vapor. The reservoir communicates with a medication metering assembly consisting of a fixed volume accumulator positioned between a pair of valves. The valves alternately open and close to admit medication from the reservoir into the accumulator and to dispense a precise volume spike to an outlet catheter. The unit is externally programmed. As background to the Prometra® pump is U.S. Pat. No. 5,049,141.
Multiple medications are often put into implantable pumps to treat certain specific conditions. For example, morphine may be used to treat the nociceptive pain and a local anesthetic (such as bipuvicaine) may be used to treat a neuropathic pain component. The use of multiple medications in single drug reservoir presents difficult clinical and medical device challenges. The mixture of drugs may present drug stability issues and a complex dosing challenge given the varying concentration and administration rates for each drug.
In U.S. Patent Publication No. 2007/0073230 to Jasperson et al., entitled “Drug Infusions System with Multiple Medications”, a system intended to minimize the danger for confusion and error in dosing multiple drugs from a common reservoir is described. More than one drug in the reservoir of the implantable infusion device substantially increases patient dosing difficulties. The clinician not only must program the device to perform a series of steps in order to deliver one drug to the patient, but must also take into account the affect of creating or modifying a program for one of the drugs on the delivery of all other drugs also contained within the same reservoir. Jasperson's system determines the resultant dose of a secondary dose based upon changes in primary drug dosage rates and displays it to the clinician.
In U.S. Pat. No. 7,083,593 and U.S. Pat. No. 7,192,414 to Stulz, each entitled, “Programmable Implantable Pump with Accessory Reservoirs and Multiple Independent Lumen Catheter”, an implantable pump with multiple chambers or reservoirs for storing drugs, each coupled to a dedicated pumping mechanism and outlet catheter is disclosed. The device does not permit the mixing and/or dilution of medication. Separate pumping mechanisms affect device reliability and manufacturing efficiencies.
Tucker et al. in U.S. Pat. Nos. 4,193,397 and 4,258,711, entitled, “Infusion Apparatus And Method”, disclose a dual reservoir implantable pump with an accumulator—a basal reservoir containing medication of a certain dosage and a smaller bolus reservoir containing high concentrate medication. The basal reservoir discharges medication at a constant specified rate. The bolus reservoir discharges the high concentration of medication to a smaller accumulator and, at a specified time, the accumulator discharges the bolus dose into a chamber where it is combined with the basal medication discharge. Combined dosing is not simply the instantaneous sum of the basal and bolus rates, it is a complex function of reservoir volumes, infusate concentrations, flow path resistance, mixing chamber volume, outlet tube volume and valve-on time. The bolus dose cannot be administered separately unless the basal reservoir is empty nor can it be mixed or diluted by the basal medication.
In U.S. Patent Publication No. 2005/0070875 to Kulessa, entitled, “Two-Compartment Reduced Volume Infusion Pump”, a dual reservoir infusion pump is disclosed wherein small amounts of concentrated medication are mixed and diluted in a mixing chamber with a carrier prior to being released into the patient. Various challenges and methods to control dosages are disclosed including: diameter of flow path conduits, flow restrictors for either or both medication and/or carrier pathways, and discharge rates. Dosing flexibility is therefore limited by the selection of manufacturing components. Separate pumping mechanisms affect device and manufacturing efficiencies. The pump is not designed to deliver multiple drugs.
In U.S. Patent Publication No. 2006/0271022, to Steinbach and Lederer, entitled, “Multi-Reservoir Implantable Pump with Variable Flow Rate Capabilities”, a constant flow pump with two reservoirs capable of infusing two different drugs is described. It is a three chamber device with an outlet in fluid communication with the two chambers that are drug reservoirs. One of the chambers is pressurized and juxtaposed between the drug reservoirs. A flow restrictor leading from each reservoir regulates the flow of medication from that reservoir to the patient. Reservoir flows rates cannot be changed and they are variable only to the extent an election is made to use one or the other drug reservoir (if the restrictors are different) or if both chambers are filled with drugs. A mixing and/or dilution mechanism is not included.
There is a need in the art for an implantable infusion device with multiple medication reservoirs that is capable of delivering easily dosed medication from any one or any combination of reservoirs without complex pumping and flow control mechanisms and which optionally has the capability of mixing and/or diluting medications.